Projection stencil assembly

ABSTRACT

A recording system wherein a character disc or the like having transparent light modulating patterns thereon is rotated through an exposure zone so that selected patterns may be projected by the energization of a flash lamp. The projected pattern is collimated and directed to a recording zone through which move lens-mirror units at a constant speed that intercept the projected pattern and focus it onto a photoreceptive recording medium. The patterns are arranged on the character disc in spiralled configurations such that as the disc is rotated the first and last patterns of a spiral move through a fixed exposure zone at different positions relative thereto.

United States Patent 1 Mason 1 Aug.7, 1973 PROJECTION STENCIL ASSEMBLY[75] Inventor: Lawrence J. Mason, Webster, N.Y.

[73] Assignee: Xerox Corporation, Stamford, Conn.

[22] Filed: Dec. 23, 1970 [21] Appl, No.: 100,988

Primary Examiner-Robert P. Greiner AttorneyJames J. Ralabate, John E.Beck and Benjamin B. Sklar [57] ABSTRACT A recording system wherein acharacter disc or the like having transparent light modulating patternsthereon is rotated through an exposure zone so that selected patternsmay be projected by the energization of a flash lamp. The projectedpattern is collimated and directed to a recording zone through whichmove lens-mirror units at a constant speed that intercept the projectedpattern and focus it onto a photoreceptive recording medium. Thepatterns are arranged on the character disc in spiralled configurationssuch that as the disc is rotated the first and last patterns of a spiralmove through a fixed exposure zone at difierent positions relativethereto.

5 Claims, 7 Drawing Figures PATENIEDAUB' 7 I975 SHEET 1 [If 6 INVENTORLAWRENCE J. MASON PAIENTEU AUG 709 15 SHEU 2 0F 6 PAIENTEU AUG 71975SHEET 3 [IF 6 PAIENIH] AUG 7 I973 SHEET 5 [IF 6 IN SYNC D A o L G E R Z-REG.

REG. LOAD FIG. 6

PATENIED AUG 7 I975 snzusnre FIG. 7

1 PROJECTION STENCIL ASSEMBLY BACKGROUND OF THE INVENTION ble ofhighquality recording at a speed much greater than conventional priorart recorders. A particular problem area is the accurate positioning ofcharacters along a line of recordedinformation. More specifically,non-uniform spacing has occurred in less sophisticated recordersdue tocharacter size variations and the inexact incremental drive systemsused. for advancing an appropriate optical system. In efforts toovercome this deficiency, prior art techniques have involved complexcoding of a character disc ina binary fashion, for example, to indicateparticular spacing information corresponding to that particularcharacter. However, such complexity has detracted from the reliabilityof the recorder itself and has increased its cost as well.

The present invention permits ,a constantly driven optical system withthe assurance thatfthe inter-character spacing will be uniformthroughout while making recording rates of at least 300 characters persecond possible with typewriterquality.

Therefore, it is anobject of the present invention to improve opticalprojection recording.

It is another object of the present invention to provide an improvedcharacter disc assembly which insures uniform spacing of charactersacross a line of recorded information with a minimum of complexity andcost without sacrificing recording speed.

It is an additional object of the present invention to provide animproved character disc or drum which employs a simplified codingtechnique for proper spacing of characters in the final recording.

These and other objects which may become apparent may be appreciatedmore readily upon reading the following detailed description inconjunction with the attached drawings forming a part hereof.

DETAILED DESCRIPTION OF THE DRAWINGS FIG. 1 is a side view of anapparatus in which the present invention may be utilized;

FIG. 2 is a front view of the apparatus of FIG. -1 with some partsbroken away;

FIG. 3 is a top. cross-sectional view of FIG. 2 taken along sectionlines'33; I

FIGS. 4 and 5 illustrate sequential relationships between the characterdisc and the optical field stop disc for projecting properly spacedcharacters and projecting only one character at a time;

FIG. 6 is a schematic representation of the logic circuitry whichcontrols the apparatus employing the present invention; and,

FIG. 7 is a plan view of a modified character disc and stationaryaperture mask embodying the present inventive concepts.

Reference will not be made in detail to themechanical structuresillustrated in FIGS. 1, 2 and 3 which'depict in detail the significantportions of a character recorder in accordance with the principles ofthe present invention.

DETAILED'DESCRIPTION OF THE PREFERRED EMBODIMENT FIG. 1 shows insomewhat more detail than FIGS. 2 and 3 exemplary xerographic processstations which are conventional in nature and actually form no part ofthe present invention. However, they are illustrated to provide a pointof reference for the present invention in a practical environment. Notall of the details of the xerographic process have been illustrated butsufficient details of those stations illustrated and other desirablestations not illustrated may be obtained from US. Pat. No. 3,187,651,which issued to Eichorn et al. on June 8, 1965, assigned to the sameassignee as the present application. Basically, a conventionalxerographic drum 2 is shown to rotate in the'direction indicated by thearrow to pass successive portions under the influence of a pre-exposurecorotron 4 and to an exposure station which is represented by the slitmask 6 where the previously charged xerographic drum is selectivelydischarged in accordance with the intensity of the image at the exposurestation. The latent electrostatic image thereby'produced may then beconventionally developed with electroscopic marking particles using asuitable developing apparatus such as a cascade developer represented bythe housing 8. v I

The developed latent image is then moved to a transfer stationwhere atransfer corotron 10 transfers the electroscopic marking particles ontoa, copy sheet which is held on a copy sheet conveyor l2 by means of asuitable gripper mechanism 14 shown in more detail in the aforementionedpatent. The copy sheet can originate from an appropriate copy sheet tray16 under the influence of a feed-out roller 18 and paper guides 20.After transfer a conventional radiant fuser 22 may be employed topermanently affix the transferred image onto the copy sheet.

Referring now specifically to the mechanical structure with particularreference to FIG. 2 which best depicts this structure which is partiallyshown in FIGS. 1 and 3, the xerographic drum 2 which is rotated bymotive power applied to its shaft 24 provides the final receptor ofoptical information projected onto it via slit mask6.

As noted before, the xerographic aspects of the present disclosure donot constitute a portion ofthe inventive concept herein disclosed. Forexample, any photoresponsive medium may be used to receive and recordthe optical projections. Therefore, the" xerographic drum maybe'replaced by a suitable photographic rnedium or any other lightresponsive medium. It goes without saying that in certain situationsdepending upon the type of recording medium utilized a drumconfiguration is'not necessarily desirable and a flatplate adapted formovement could also be employed.

The source of the optical projections which are received by thexerographic drum 2 originate, in one embodiment, from a pattern disc 26which is driven rotatively so as to pass an annular pattern area'28successively through an exposure zone. As will be described hereinafter,this area 28 is composed of sets of transparent light modulatingpatterns. The exposure zone is aligned with the center line of the imagepath designated in FIG. 2 by reference numeral 30. Otherelements furtherdefine this exposure zone such as the optical field stop disc 32 whichis driven about its axis represented bya drive shaft 34 as shown in FIG.2. As

shown best in FIG. 3 the optical field stop disc 32 is generally opaqueto a particular illumination utilized in the recording apparatus and hastransparent portions 36 thereon which correspond to segments of aspiral. Each segment 36 has a radius from the center of the disc 32which corresponds to the following equation:

where R is the radius of the segment measured from the center of thedisc 32, R is the shortest radius of the segment as measured from thecenter of disc 32, K is a constant and 0 is the angle subtended by R andR0. As shown in FIG. 3, disc 32 has three such segments 36, each ofwhich corresponds to a set of light modulating patterns on disc 26 whichare used in the recording operation. In a particular example of thisdisclosure, each set includes alphanumeric characters comprising twoalphabets, upper case and lower case.

As will be seen again in FIG. 3 referring to the disc 26, there arethree transparent slits 38 in an otherwise opaque disc with, of course,the exception of the character area 28 and other slits. These slits, aswill be seen in more detail hereinafter, designate the beginning and endof an alphanumeric character set on the disc 26. Each slit 38 is spaced120 apart from adjacent slits and consequently the angle subtended byany one of the segments 36 on the optical field stop disc 32 is equal to120. Therefore, as shown in FIG. 3 where the character area 28 of disc26 and any portion of a segment 36 of disc 32 intersect proximate to thecenter line 30 of the image path, the exposure zone will be defined. Itcan be readily understood that although the character area 28 isconcentric about the axis and drive shaft 40 of character disc 26, theexposure zone previously defined will vary about the center line 30 ofthe image path as a function of the aforementioned equation since thespiral segments 36 will vary in their distance from the center of disc32. This will be seen in greater detail hereinafter in connection withdiscussion of FIGS. 4 and 5. It is sufficient at this time to describethe exposure zone as being the intersection of any of the segments 36and the character area 28 of disc 26 at or near the center line 30 ofthe image path.

Both disc 32 and 26 may be formed by etching photographic emulsion whichis adhered to one side of a lightweight normally transparent disc-shapedmaterial such as plexiglass. The emulsion side of the discs 26 and 32face each other and are very closely spaced so as to permit the segments36 and the character area 28 to be as proximate to the object plane ofthe projection optical system as is possible.

This projection optical system is represented by a collimating opticalassembly generally designated by reference numeral 42 which acts tocollect the light passing through the selected portion of the characterdisc 26 and collimate it for reflection by a main mirror 44. The lightfrom main mirror 44 is then acted uponby two identical lenses 46. Thesemay be achromatic doublets of conventional design and as seen in FIGS. 1and 3 are substantially rectangular in area. They serve to focus viamirrors 48 the light reflected by mirror 44 onto the image planerepresented by the surface of xerographic drum 2 exposed through slitmask 6. As is shown in FIG. 2, a support member 49 holds the lens 46 andthe mirror 48 in a fixed relationship relative to each other to insureproper optical alignment throughout the operation of the apparatus.

The source of the light which has been described as passing through theoptical system is generated by a suitable flash lamp 50 which maysuitably be a xenon lamp housed in a conventional light box 52 so as topermit light to exit through an optical assembly 54 and into theexposure zone previously referred to.

The description of the optical arrangement can be summarized bysaying'that a character in the pattern area of disc 26 is illuminatedand this object character in the character plane-is imaged at infinityby the collimating action of assembly 42. The main mirror 44 reflectsthis collimated light to lens 46 which images that character via mirror48 onto the image plane at the surface of the drum 2 or otherphotoreceptor.

Referring now specifically to FIGS. 1 and 2, the manner in which theoptical projections from the character disc 26 are spatially recorded onthe surface of drum 2 will be described. As noted hereinabove, lens 46and mirror 48 are formed into an integral unit by an appropriate supportmember 49. This support member is, in addition, attached to a carriage56 which is fixed to a flexible, endless drive member 58, which may be achain as illustrated in the drawings. The chain engages two sprocketwheels 60, one of which may be driven by a suitable source of motivepower not shown to move the chain 58 through its particular path asshown best in FIG. 2. A plurality of carriages 56 are shown attached tothe chain 58 and, as will be seen hereinafter, this number of suchcarriages and associated .optical units can not be less than two and maybe larger.

FIG. 2 depicts two of these units in the optical path formed by thereflected light from mirror 44 which in part is directed by either oneof the units onto the surface of drum 2 at the beginning or end of theslit in the mask 6. The movement of the chain viewing FIG. 2 is in aclockwise direction as indicated by the arrows. Therefore, thelens-mirror assembly on carriage 56 on the left can be considered ashaving completed the projection of a line of alphanumeric informationand the identical assembly on the right can be considered as initiatingthe next line of recorded information. Because of the finite speed atwhich chain 58 drives these lensmirror assemblies along the axis of drum2, it is necessary in order to achieve line recordings which aresubstantially perpendicular to the edges of drum 2 to skew the plane ofthe chain 58 with respect to the drums axis which is represented in FIG.3 by reference numeral 62. The amount of skew is a function of thechains speed and the linear velocity of the drum. In this way,

in the final copy the horizontal lines of alphanumeric information willbe equally spaced and substantially perpendicular to the side edges ofthe copy sheet.

Because of the high speed capabilities of the recording apparatuspermitted by the present invention the speed at which the chain 58 isdriven may cause certain vibrations which adversely affect the qualityof the final copy. In order to minimize these effects, a stabilizingplate 64 is employed upon the edge of which in effect rides carriages 56by way of wheels 66 which are best shown in FIGS. 1 and 2. These wheelsare rotatively mounted on the same pins which attach carriage 56 to thechain 58. Because of the tension in the chain 58, the wheels 66 of thecarriages 56 maintain continuous contact with the edge of thestabilizing plate 64.

In the recording zone of the apparatus defined as shown in FIG. 2 bythat space between the mirrors 48 of the two lens-mirror units shownproviding exposure of the drum 2, additional stabilizing flanges 68 areemployed to provide positive restraint on both the upper and lowerportions of the periphery of wheels 66. As seen better in FIG. 1 flanges68 are attached appropriately to respective ones of the stabilizingplates 64. This insures the very minimum of vibration in the recordingzone by chain 58 and carriages 56 thereby providing little, if any, blurin the image projected onto the surface of drum 2. It is recognized thatthe stabilizing provisions are not necessary to the operation of thesystem but only enhance the quality of the resultant recording.

At this point, the operation of the apparatus as depicted in thedrawings may be summarized as follows.

Through appropriate logic control circuitry yet to be described, inputsignals representative of alphanumeric information are received by therecording apparatus and decoded so as to indicate what particularalphanumeric character is to be projected and recorded onto the surfaceof xerographic drum 2 at any instant of time. This indication iscompared with the ever changing status of the character disc in theexposure zone so that when the selected character is properly positionedat this zone, the flash lamp 50 is energized. The image of the selectedcharacter is then projected through the optical system via opticalassembly 42, mirror 44, lines 46, and mirror 48 to selectively dischargethe xerographic drum in accordance with the optical information. Duringthis time one of the lens-mirror assemblies on carriage 56' is movingfrom right to left as seen in FIGS. 2 and 3 so that a series or sequencyof alphanumeric characters may be recorded in a line substantiallyparallel with the axis of drum 2.

Due to the speeds involved, it is necessary to provide proper anduniform spacing between adjacent alphanumeric characters appearing in aword, for example. Since the motion of the driving chain 58 is at aconstant velocity in contradistinction to being incrementally stepped,it is possible when using prior art techniques that two alphanumericsymbols separated by some distance on the character disc 26.may berecorded 'sequentially with a spacing which would be different from thespacing between two projected characters which occupy adjacent positionson the disc 26. Expressed differently, since the disc 26 is continuouslyrotating at a uniform speed, the time which elapses between thecharacter A, upper case, being at the exposure zone and the lower case Zbeing at the recording zone is considerablygreater than the timeelapsing between the upper case A and B sequentially being presented tothe exposure zone. Since the carriages 56 are moving constantly, thisdifference in time means the lens-mirror unit moves a different amount.

As will be seen in more detail in the description of the electroniccircuitry which controls the recording process, the apparatus of thepresent invention is designed to project one alphanumeric character perset of alphanumeric characters. Therefore, the spacing problem isinvolved each time it is desired to sequentially record any twocharacters.

However, the present invention solves this problem by utilizingcharacter slits shown best in FIGS. 4 and 5 to which reference is nowmade. As shown there, each slit is on a radian of disc 26 and extendsfrom the periphery of disc 26 a short distance toward the center of thedisc. Each alphanumeric character in the area 28 is centered in acharacter space which is uniform in size for all characters. Therefore,the center of adjacent characters are uniformly spaced from each other.The character slits vary in their alignment with a particular characterspace. As will be noted the spacing of adjacent character slits isuniform. However, the spacing or the slignment between a particularcharacter slit and its respective character space varies depending uponthe position of the respective character in its respective set. This canbe seen upon close examination of FIGS. 4 and 5.

Character slit 69 associated with the space occupied by the upper casecharacter A is located 0.5/52 of a character space to the right of theleft-most portion of that character space. Examining the character slit70 associated with the space occupied by the upper case character M itcan be seen that this slit is removed from the left-most portion of thatspace by slightly less than one-fourth of the width of that characterspace. In FIG. 5 the character slit 72 associated with the lower casecharacter M is shown to be removed approximately three-fourths the widthof a character space from the left-most side of the character spaceoccupied by this character. Turning then to the lower case character Z,character slit 74 associated with that character is located 0.5/52 .of acharacter space to the left of the right-most side of that space. Thecharacter slits for those alphanumeric characters intermediate thecharacters previously referred to have associated with them similarslits which are positioned uniformly from the preceding slit.

The changing relationship of successive character slits withsuccessivecharacters is easily appreciated when it is considered that eachalphanumeric character both upper and lower case is centered in auniform sized character space. The character slitsas noted previouslyare uniformly spaced from adjacent slits but the spacing of these slitsis somewhat greater than the spacing between the centers of adjacentcharacter spaces. Therefore, in the example used in this descriptionwherein each alphanumeric character set contains 52 symbols orcharacters plus one blank space and the center of adjacent charactersare spaced apart by a unit designated by the constant Q, the characterslit spacing between adjacent slits can be represented by Q/52 plus Q.Therefore, referring to FIGS. 4 and 5, it can be as-' v certained thatif character slit 69 associated with upper 1 case character A is alignedwith an initial or zero position then character slit 70 associated withthe character upper case M is then spaced along the periphery of disc 26from character slit 69 by an amount equal to 12 (Q/52 Q). In alikemanner character slit 72 associated with lower case character M isspaced-from character slit 68 by an equal amount to 38(Q/52 Q) andcharacter slit 74 is similarly spaced from character slit 69 by anamount equal to 51(Q/52 Q).

Having described the unique relationship between a particular characterslit and its respective, character space with which it is associated,the function of these character slits in accordance with the presentinvention willnow be described. As noted hereinabove, the various slitsreferred to, both the character slits and slits 38 on the character disc26, are transparent areas in the normally opaque surface of the emulsionside of the character disc 26. Therefore, these slits transmit lightfrom an appropriate source of constant illumination which is not shownin the figures but may be a conventional low voltage lamp. The lightwhich is transmitted by these particular slits is detected by aconventional pair of photocells or photodiodes which are located insidethe photocell assembly designated by reference numeral 78. One photocell(referred to hereinafter as the clear photocell) exclusively monitorslight passing through slit 38 while the other photocell (referred tohereinafter as the character photocell) monitors exclusively lightpassing through the character slits. As will be seen hereinafter inconnection with the description of the logic control circuitry, slit 38is utilized to generate a signal to reset or clear a character counterwhich generates a full count when the selected character is in theexposure zone. As can be seen from the depiction of FIG. 3, thephotocells are located 120 degrees from the center of the exposure zoneor from the center line 30 of the image path. This is done so as toremove the photocells from the exposure zone so that they will notobstruct the light passing therethrough. Placing them 120 from thisposition is equivalent to their being at this position since threecharacter sets are used on the character disc 26. When, for example, thecharacter photocell detects character slit 70 as shown in FIG. 4, thecontrol logic through the use of a counter, which at this pointregisters a full count, knows that the upper case character M is in theexposure zone. As noted hereinabove, the exposure zone is actuallydefined by the intersection of the character area 28 of character disc26 and a portion of one of the spiral segments 36 of the optical fieldstop disc 32. As shown in FIG. 4 this exposure zone may extend anywherefrom the point represented by reference numeral 80 to the pointrepresented by reference numeral 82. This space between these two pointsalong a radian of disc 26 passing through center line 30 of the imagepath defines the upper and lower limits of the exposure zone.

As will be brought out in the discussion of the logic circuitry, thecount of the character slits determines precisely when the flash lamp 50will be triggered. Since the position of character photocell in assembly78 is fixed relative to the center line 30 of the image path, thecharacter slit associated with the particular character in the exposurezone which is porjected by the light from the flash lamp 50 will alwaysbe in the same position relative to center line 30 and coincidenttherewith. However, because of the unique relationship between aparticular character and its respective character slit, the position ofthe projected character in the exposure zone will vary. For example,when the flash lamp is triggered to project the image of the upper casecharacter A, the character itself will be to the right side as FIGS. 4and 5 are viewed of its respective character slit and of the exposurezone. In other words, the projected character will be closer to point 80as shown in FIG. 4 than point 82. In the other extreme, when lower casecharacter Z is projected, it will be to the left, as FIGS. 4 and 5 areviewed, of its respective character slit and closer to side 82 of theexposure zone than side 80 thereof.

The particular function of the character slits is best explained inrelation to actual operating parameters within which the apparatusillustrated is capable of operating. An initial factor which is fixed invalue is the bit rate possible for transmission over standard voicegrade telephone lines, viz., 2,400 bits/second. Typical alphanumericcodes use 8 bits/character which dictates a maximum transmission andrecording rate of 300 characters/second. Since character disc 26 carriesthree character sets and one character per set is projected the discmust rotate at a rate of I00 revolutions/- second in order to achievethe 300 character/second recording rate (3 characters/revolution is themaximum recording rate). For typical typewriter spacing, l0character/linear inch of drum surface is required. If 84 characters aredesired per line then the recording zone limited by slit mask 6 is 7inches. This results in a drive speed for chain 58 of 25 inches/second.At this speed, the chain, and hence the optical units attached thereto,will progress approximately one character space during the time disc 26moves the equivalent of one character set through the exposure zone.This is realized when it is considered that the chain 58 moves at therate of 300 character spaces/second while disc 26 moves one characterset through the exposure zone in one three-hundreth of a second at therate of I00 revolutions/second.

With the preceding factors and parameters understood, the problem ofuniform spacing of recorded characters can be better appreciated. Sincethe tangential velocity of a typical 4 inch diameter disc isapproximately 1,200 inches/second, one aspect of the spacing problem isoverlap in the recording of two characters on the disc occurring veryclose to one another, e.g., lower case character Z and upper casecharacter A. The amount of time elapsing between the projection of thesetwo characters is so small as to be negligible for practicalconsiderations. However, in-spite of this fact, proper spacing of thesetwo characters is accomplished in accordance with the principles of thepresent invention. Let the center of the exposure zone which correspondsto the center lines 84 and 86 in FIGS. 4 and 5 represent a zeroposition. To the left of this zero position are negative values ofdistance and to the right thereof positive values. These negative andpositive values relate distance of the center of a character space fromits associated character slitwhen that character slit is at the zeroposition (when the lamp is energized if it is desired to record thecharacter in that character space). Since the position of the characterspaces are predetermined relative to their character slits, a table ofdistance values can be attributed to each character in a character set.With 52 characters per set, values from +25.5 to 25.5 can be given thecharacters as follows:

as positive. Similarly, the lower case character 2 is given a value of25.5/52. Therefore, if the sequence of characters is zA, the distancebetween these two characters on the drum 2 must be equal to onecharacter space. If it is less than this amount, the recorded characterswill overlap, if greater than this amount, the spacing between therecorded characters will be incorrect. This can be expressed by thesimple equation:

D D, d l (where d distance traveled by the lens-mirror assembly).

which translates when using the above table to:

(+25.5/52) (25.5/52) +d= +l/52 +l/52 52/52=l In the sequence such as Az,it can also be demonstrated that there will be only one character spacebetween characters on the drum 2 as follows:

Again using the above Table, D, 25.5/52 and D +25.5/52. In thisparticular sequence one character space is moved by the chain 58 perpassage of a character set through the exposure zone. Therefore d willbe equal to 52/52 or one character space, as the character set includingthe blank character space containing the projected character A passesthe exposure zone, plus another amount of 51/52 required to move thesecond character set through the exposure zone to bring the lower casecharacter z thereto. So d will equal (52/52 51/52) and the three termequation translates to:

This demonstration with the two sequences of characters establishes theeffectiveness of the character slits in insuring that the space issubstantially uniform between the recording of any two characters in theset regardless of the distance separating their stencils on thecharacter disc.

With the explanation of the character disc and the function of thecharacter slits therein given above, it can be appreciated that sincethe exposure zone is actually two character spaces wide, something mustinsure that only one character is projected at a time. As FIGS. 4 and 5are viewed, it can be seen that two characters are usually in theexposure zone between points 80 and 82 with the exception of the firstand. last characters of the sets. In order to eliminate the possibilitythat two characters will be projected, optical field stop disc 32 isemployed. Its utilization can best be iseen with reference to FIGS. 3, 4and 5 which show the relationship between the two discs. Disc 32 rotatesin a direction as indicated by the arrow and has its rotationsynchronized with that of the character disc so that one of the spiralsegments 36 passesthrough the exposure zone coincidently with thepassage therethrough of one of the character sets on disc 26. This isevident from the positions of the discs as depicted in FIG. 4 or 5.While FIGS. 4 and 5 do not show two characters in the exposure zone, itcan be pictured when the character disc is advanced so that, forexample, upper case characters A and B are in the exposure zonetogether. In that situation, the optical field stop disc 32 would blockcharacter As projection and permit the projection of character B viatransparent segment 36.

From a consideration of FIGS. 4 and 5, it can be seen that the samemovement of the characters within the exposure zone as delimited bysides 80 and 82 thereof can be accomplished by a single disc 200,illustrated in FIG. 7, which disc combines the features of both the disc26 and 32. To thisend, the A of FIG. 4 when in its correct position(i.e., between the center line 84 and the side could betransferred fromthe character disc 26 to the aperture disc 32 in exactly the orientationshown. Each successive character, therefore, B, C, etc., could be alsoplaced on the aperture disc when in its correct position as it movesthrough the exposure zone. As will be appreciated the resultingcharacter set formed on the aperture disc will follow the spiral segment36 thereby resulting in a spiral segment 202 containing a complete setof characters as shown in FIG. 7. The other spiral segments would beformed in the same manner.

The resulting spiral segments each have a radius from the center of thedisc 200 which corresponds to the equation:

where R is the radius of a segment measured from the center of the disc200, R is the shortest radius of the segment as measured from thecenter, K is a constant and 0 is the angle subtended by R and R A set ofcharacter slits 204 for each character set is positioned on the disc200. Unlike the slits of the disc 26, the slits 202 are positioned inexactly the same position relative to their associated character spaces.

As shown, the same amount of area, i. e., that occupied by twocharacters, is required for illumination by the flash lamp 50.Accordingly, a fixed aperture structure 208 having an aperture 210disposed in the exposure zone will prevent adjacent characters frombeing partially projected.

Now that the mechanical aspects of the'apparatus' depicted in FIGS. 1 toshave been described, one facet of this apparatus will be explainedwhich lends it the capability of very high speed recording. Thiscapability is partially due to the role played by the moving opticalsystem comprised of the lens-mirror units including lens 46 and mirror48 attached to the drive chain 58 via members 49 and 56. However, byitself this optical system could not achieve the ultimate speedcapability but in cooperation with the collimating optical assembly 42it is all possible.

The recording zone in a typical recorder may be approximately 7 incheslong and is defined by the opening in the slit mask 6 in the directionof the drums axis.

The spacing of the lens-mirror units is such that the dis-;

tance between the focal paths in the'plane of the slit mask of the twounits closest to the recording zone is exactly equal to the dimension ofthe slit masks open- 'ing measured in the direction of the axis of therecording drum 2. In other words, viewing FIG. 2 of the two lens-mirrorunits intercepting the collimated image projection reflected by mirrorthe one on the left is focusing whatever character is being projectedonto the slit mask and the one on the right is just focusing the samecharacter image through the slit masks opening the unit on the right isjust beginning the next line of information. From this explanation itcan be appreciated that the spacing of the lens-mirror units on thedrive chain is somewhat critical.

It is helpful in the discussion to refer back to the parameters offeredto show a practical environment of the recording apparatus. In theegtample being used, the lines of alphanumeric information recorded havea vertical density of 6 lines per inch. Therefore the drum must movethrough the recording zone at approximately 0.625 inches per second.

As noted hereinabove, the spacing of the lens-mirror units alone is notenough to insure this high speed and nonexistent dead time betweensuccessive line recordings. The collimated character projection is alsoimportant. From the above discussion of the precise spacing of theselens-mirror units, it is essential that each lens 46 focuses the samecharacter being projected at that instant of time. This is made possibleby utilizing Huygens theory that the wave front of light emission can atany future time be determined by assuming that every point on a givenwave front acts as the center of a new disturbance emanating from thatpoint. In other words, a new wave front can be found by treating eachpoint of the old wave front as a new source oflight from which asecondary wavelet emanates in all directions. Therefore, when the lightemitted by flash lamp 50 is collected and translated by the opticalarrangement 54, which includes conventional condenser or collectorlenses, through the transparent character shaped area in the exposurezone, that wave front so shaped by the transparent area includes amultiplicity of individual light sources corresponding to the points ofthe characters area. These light sources radiate light in all directionsbut the collimating assembly 42 acts to collimate it so that many imagesof the projected character are focused at infinity by this assembly 42.By means of mirror 44 and lenses 46, two of these images are interceptedand focused by the two lens-mirror units as one leaves and one entersthe recording zone. In this manner, the projected character image isinstantly available to the unit on the right as the next line is beingrecorded immediately after the preceding lines recording was completed.

Having described the mechanical aspects of the present invention and thefunction of the character slits, reference will now be made to FIG. 6which schematically depicts the logic circuitry employed to control therecording process. As noted hereinabove, the apparatus of this inventioncan be used on the receiving end of a standard voice grade telephonelink over which is transmitted coded groups of binary bitsrepresentative of information or data as well as various control words.Such bit groups are received by the circuit of FIG. 6 at an inputterminal 3 which serially supplies these bits to the input of aconventional shift register 5 and to a conventional clock bit recoverycircuit 7. The latter provides suitable recovered clock pulses to acounter 9 of conventional design which has a full count capacity equalto the number of bits employed to represent a particular alphanumericcharacter. In the particular example used in this description, eightbits have been referred to as constituting a bit group. Circuit 7 alsosupplies these recovered clock pulses to the shift input of the shiftregister 5 which shift the bits of the bit group thereinto. In additionto the shift register 5 and the counter 9, the recovered clock pulsesare also provided as an input to gate 11 and detector 13.

As for the detector, these pulses actually serve to enable an input gatein the detector 13 so that the detector can decode certain code wordstemporarily stored in the shift register 5. Code words such as SYNC andSTART are decoded by this conventional detector circuit 13 which may becomprised of various gate combinations as is well known in the art. Asshown in FIG. 6, the two outputs of the detector 13 are labeled Startand Sync. Each of these outputs will be energized when the proper wordis detected as being stored in the shift register 5.

In addition to the parallel output to the detector 13, shift register 5also has a parallel output to a conventional eight stage digitalregister 15 which, in turn, has parallel outputs to another identicalregister 17 and so on until an eighth such digital register 19 isreached. These registers serve as a very short buffer for the codegroups before and during the recording process.

Before the actual recepit of coded information is described, adescription of the link between the logic circuit of FIG. 6 and themechanical side of the recording apparatus will be given. As wasdescribed in connection with FIGS. 1, 2, and 3, photocell housing 78houses two photodetectors referred to as a clear photodetector and acharacter photodetector which detect the presence of slits 38 and thecharacter slits, respectively, of the character disc 26. These twophotocells or photodetectors are coupled to suitable amplifiers 21 and23, respectively, via input terminals 25 and 27 associated therewith.

The character photocell and amplifier 23 provide a signal each time oneof the character slits passes the photocell. This signal consitutes whatwill be referred to as simply a clock pulse, in distinction to therecovered clock pulse. Such a clock pulse is supplied to manysub-systems of the circuit of FIG. 6. The character counter 29 receivesthem to index its count. In addition, the flash lamp trigger gate 31 andthe register load circuits 33 receive these clock pulses to respond in aparticular manner to be described hereinafter.

The clear photocell and amplifier 21 provide a clear signal indicativeof each time one of the slits 38 on the character disc passes housing78. These signals serve many roles, one of which is to clear or resetthe character counter 29 to its initial condition, for example, zero.The eight logic gates represented by block 35 are enabled by a delayedclear signal, which permits the complement of the contents of the eighthregister 19 to be loaded into the character counter 29. In addition,these clear pulses or signals serve as one input to gate 37 and to setflip-flop 39 for purposes to be described hereinafter.

In continuing this description of the links betweenthe mechanicalapparatus and the logic control circuit of FIG. 6, reference must bemade to output terminal 41 which, via an inverter 43, couples the outputtrigger signal generated by trigger gate 31 to the flash lamp previouslyreferred to in connection with the description of FIGS. I and 2. Also,mention is appropriate of output terminal 45 which is coupled tosuitable control relays initiating particular sub-systems in thexerographic process area such as the pre-exposure corotron andxerographic drum drive thereby preparingthe photoreceptor for therecording step as well as other drives for the chain 58 and discs 26 and32.

In operation, the circuit of FIG. 6 receives sync bit groups first whichare shifted into shift register 5, detected by detector 13, andindicated as a pulse to an in sync circuit 76 which may be of anysuitable design to monitor a sequence of received sync pulses. An insync condition is indicated by a signal at terminal 51 which can becoupled to other circuits responding to such a condition. This in syncsignal is provided to reset all the flip-flops included in the registerload circuits 33 as well as flip-flops 55 and 57. By way of inverter 59coupled to terminal 51, an inverse signal of opposite polarity to thatof the in sync signal is supplied to reset flipflop 61. Practically,this means that once the recording apparatus reaches an in synccondition, the flip-flops mentioned above as being coupled to terminal51 are placed in an initial reset condition.

After this in sync condition is reached, a START word is transmitted tothe recorder which, like the SYNC words, is shifted into shift registerand detected by detector 13. It should be noted that because of thedesign of the logic controlling the loading of the eight digital orbuffer registers, none of the SYNC words are initially'translated tothese registers from the shift register 5. The same is true for thisfirst START word. However, this first START word does act to enable gate11 and, upon the trailing edge of the output signal therefrom, placesflip-flop 55 in a set condition. This occurs on the trailing edge of oneof the recovered clock pulses. However, due to the propagation timeinherent in the flip-flop 55 gate 63 remains disabled. As noted beforein connection with output terminal 45, this first START word is requiredwhen a xerographic recording medium is utilized to permit preparation ofthe xerographic process stations. In addition, the level at outputterminal 45 is also used to begin the chain drive which moves thelens-mirror units through the recording zone.

After the first START word, additional SYNC words may be transmitted andthen the second START word is sent. This word is decoded by detector 13and gate 11 is once again enabled. However, since the reset input offlip-flop 55 is wired directly to ground potential, the output of gate11 has no effect on its set condition in which it remains. But theenabling of gate 11 does effect the enabling of gate 63 and, upon thetrailing edge of the pulse at its output, flip-flop 57 is set. Thisgenerates a high level signal at its set output which enables one inputof gate 65. I

The other inputs to this gate 65 originate from the counter 9, characterphotocell amplifier 23, and latch 67 consisting of gates 69 and 71. Thefirst twoof these inputs can be considered at a high level. As forthelatch, its gate 69 monitors two inputs: one from counter 9 and the otherfrom gate 71. This second gate 71 monitors the output of gate 69 and thereset output of flipflop 53 in the register load circuit33 whichcontrols the loading of the second buffer register 17. Sinceflip-flop 53is initially in a reset condition by action of the in sync signal, itsupplies a high level signal to gate 71. The results of these inputs onlatch 67 is to provide a high level signal to gate 65 to be translatedinto a trailing edge by gate 65 and inverter 73 thereby setting flipflop61. A high level condition is then created at the output side ofinverter 75, the input of which is coupled to the output of gate 77.This high signal is sufficient to enable the loading of the first bufferregister with the contents of shift register 5. This would be-the firstcharacter after the second START word.

Before detailing the action of the register load circuits 33, it maybehelpful to briefly describe their function. Once a word is loaded fromthe shift register 5 into the first buffer register 15, the loaded wordthen effectively slides" through the buffer registers until it reachesthe last, or eighth register in the example of FIG. 6, or an emptyregister immediately upstream from a loaded or full register. How thisis accomplished will now be described. For simplicity and ease ofunderstanding the circuit of FIG. 6, not all of the circuits 33 havebeen illustrated in the same detail as the first one. It is to beunderstood that each such circuit associated with the buffer registers(with the exception of register 19) has the same design as the onedetailed in FIG. 6 in the dashed block 33.

With the output of gate 77 experiencing a level transition from high tolow, to high, the output of gate 79 goes high and then low providing atrailing edge of the toggle input of flip-flop 53 thereby setting thisflip-flop. This trailing edge coincides with the trailing edge of one ofthe clock pulses supplied to gate 65. With flipflop 53 set, the outputof latch 67 goes low effectively disabling gate 65. Also, via inverter81 coupled to the set output of flip-flop 53, a resetting pulse issupplied to flip-flop 61. v k

Gate 83 monitors the clock pulses, the set output of flip-flop S3,andvan output from the next circuit 33 downstream. This output comesfrom the reset output of the flip-flop included in that particular loadregister circuit 33. Since that flip-flop would be initially in a resetcondition, this is a high level'signal. Therefore, with flip-flop 53 inan initially set condition, the output level of gate 83 goeshigh-low-high and, accordingly, the output level of inverter 85 goeslow-high-low providing an enabling pulse to the second buffer register17 to permit the word to continue its slide toward the last of thebuffer registers. This same operaton continues to let the word go' fromone buffer register to the next succeeding one until it ends up in theeighth register 19. Meanwhile, with the high-low-high sequence from theoutput of gate 83 and a high signal from gate 77, the output of gate 79goes low-high-low providing a resetting edge to the toggle input offlip-flop 53, thereby preparing it for the next received bit group atinput terminal 3.

This same preparatory cycle is accomplished in the remaining circuits 33by the action of gate 83 as con veyed bythe output therefrom which is aninput to gate 79s counterpart iri cuit 33. g

' Thetechnique of loading the last or eighth register 19 differssomewhat from that which has been described in connection with the otherbuffer registers. The loading of this register 19 is controlled in thefirst instance by gate 87 which has two -inputs;.from two other'gates 89and 91. When either of thesetwo gates generates a low level signal atits input to gate 87, then a load pulse will be generated by the latterto loadregister 19. As seen from FIG. 6, gate 89 monitors an output fromthe preceding register load circuit 33 which comes from inverter 85'scounterpart therein. In addition to this, it monitors the reset outputof flip-flop 93. As will be seen hereinafter, this flip-flop is in areset condition at this time and hence a high level signal is at one ofthe inputs to gate 89. Since the output of the inverter in the circuit33 just upstream from the last register goes through the same levelchanges as was described in connection with inverter 85, that input togate 89 will experience a lowhigh-low level transition. During the highlevel, the output of gate 89 will be low thus providing a high level thenext successive downstream cirload pulse at the output of gate 87effecting the loading of the last register 19.

As the inverter in the last circuit 33 goes through the low-high-lowsequence of level changes, a trailing edge is coupled to the toggleinput of flip-flop 95 which acts to set this flip-flop. This puts a highlevel signal on the input of gate 37 coupled to the set output of thisflipflop 95. This gate 37 has two other inputs, one of which comes fromthe set output of the flip-flop in the last circuit 33. The other inputis from the clear photocell amplifier 21.

The role of gate 37 is to indicate to flip-flop 93 when the last twobuffer registers are loaded so that the recording process can begin.

This signal from gate 37 is not translated to flip-flop 93 until acharacter set begins its pass through the exposure zone previouslydescribed, i. e., a clear signal is supplied to gate 37 from the clearphotocell. At this point flip-flop 93 will be set and a signal willemanate from the set output of this flip-flop and be translated to oneinput of gate 97. Before following through the explanation of this gateand its other input, reference should be first made to what other eventstake place at the initiation of the signal.

As noted hereinabove, the clear signal clears the character counter 29after a predetermined time from which, dictated by delay circuit 99, thecomplement of register 19 is transferred or loaded into counter 29 viagates 35 enabled by the delayed clear pulse.

The complement of the register 19, when once loaded into the charactercounter 29, is augmented by one as each character in the particularcharacter set passes through the exposure zone. The code for thecharacters is so chosen that when the counter reaches its full count,the character represented by the code word in register 19 will be at theexposure zone. For example, if the desired character to be recorded wasan upper case character M, then its code or bit group could be 00001 101which would have slid into register 19. Upon the generation of the nextclear pulse, the complement of this number, 111 10010, would be loadedvia gates 35 into the character counter 29. As each character in the setpassed the character photocell, its respective character slit would bedetected and a clock pulse generated which would be supplied to counter29 to increase its contents by one. Therefore, after l3 character slitswere detected and the upper case character M was at the exposure zone,the contents of the counter 29 would be 1111111] or a full count. Thiscondition would be detected by a series of gates represented in FIG. 6by block 101 and indicated by a full count signal supplied to thetrigger gate 31. The other inputs to this gate need be satisfied beforethe character in the exposure zone would be projected onto thexerographic drum 2 by lamp 50.

One input is from flip-flop 103 which is set upon the coincidentoccurrence of two events: a signal from flipflop 93 and a high levelsignal from input terminal 105. This latter signal can be generated inseveral ways and is used to insure that the moving optical systems willbe in the right position relative to the recording zone when projectionbegins. Therefore, a microswitch or photocell system can be used toinsure that when this signal is generated the chain 58 is in apredetermined position.

Another input to the trigger gate 31 is from the clock pulse source,character photocell amplifier 23.

The final input to this gate comes from the output of gate 107 whichmonitors the reset output of flip-flop 39 and the output of trigger gate31 itself. The output of trigger gate 31 is normally high and flip-flop39 is set by the clear pulse from amplifier 21.

Therefore, all inputs to gate 31 are high thereby providing a low levelsignal at its output which is inverted by inverter 43 and translated tolamp 50 via output terminal 41 as a high level signal. The upper casecharacter M is then projected onto the recording medium.

When the lamp is flashed, a low level pulse disables gate 107 andtriggers monostable multivibrator 109 which, in turn, disables gate 91.Since the'automatic set and reset inputs of the flip-flops used in FIG.6 are level sensitive, during the disabled condition of gate 91,flipfiop 39 is reset. In addition, flip-flop is reset. Since the resetoutput of the flip-flop feeds back to the next preceding register loadcircuit 33, specifically as one input to gate 83 and the input gateassociated with the input of flip-flop 53 therein, the output of thisgate 83 goes low permitting the output of its respective gate 79 to gohigh providing the penultimate buffer register with a loading pulse.Coincidently with this, the low level pulse from gate 91 also issupplied as one input of gate 87 thereby permitting this gate to supplythe last register 19 with a load pulse also so that it can accept thecontents of the penultimate register.- It may be noted that affirmativeloading is used in the stream of buffer registers so that zeros can beloaded from one register to another without first clearing the latter.

Before the above description was started using the upper case characterM as an example, the first word .was located in the last register.Therefore, suitable detecting gates can be incorporated into detector110 which monitors the contents of register 19. The detector alsodetects other control words such as SPACE, STOP, and SYNC. When itdetects one of thesewords, it translates an inhibit signal to outputterminal 41 which effectively inhibits the energization of the flashlamp even though all conditions at the input to gate 31 are satisfied.

The above description of a high speed alphanumeric recording apparatusin accordance with the principles of the present invention fulfills allthe desirable requirements of a high speed recorder that meets thestandard of typewriter quality and versatility. 1

While the foregoing description has referred to optically detectableslits in the character disc--26, other dc tectable indicia mayv also beused, for example, conductive areas, embossed areas, or any other typeof readily detectable marking or.index.. a I I 1 While the invention hasbeen described withreference to a preferred embodiment, it will beunderstood by those skilled in the art that various changes may be madeand equivalents may be substituted for elements thereof withoutdeparting from the true spirit andscope of the invention.

What is claimed is:

1. Character projection apparatus comprising:

a character disc having a set of characters arranged in a spiralconfiguration relative to the center of said character disc, eachcharacter being spaced apart less than one character space;

a selectively fiashable light source disposed adjacent one surface ofsaid disc; 7

means adjacent the opposite surface of said disc for collimatingillumination passing through said disc;

acter disc has a plurality of sets of characters uniformly spaced onsaid disc.

4. Structure as specified in claim 2 wherein, the radius of said spiralconfiguration relative to the axis of said disc is equal to R K0,

where R, is the shortest radius of said configuration,

K is a constant, and 0 is the angle subtended by the radius of saidspiral configuration and R 5. Structure as specified in claim 4 whereinsaid characters are transparent.

1. Character projection apparatus comprising: a character disc having aset of characters arranged in a spiral configuration relative to thecenter of said character disc, each character being spaced apart lessthan one character space; a selectively flashable light source disposedadjacent one surface of said disc; means adjacent the opposite surfaceof said disc for collimating illumination passing through said disc;means for focusing said characters of said disc onto a photosensitivesurface, and means for moving the first character of said set past saidlight source at a first fixed position relative thereto and the lastcharacter of said set past said light source in a second positioncontiguous said first position.
 2. Structure as specified in claim 1including, a stationary aperture for preventing projection of more thanone character at a time.
 3. Structure as specified in claim 2 whereinsaid character disc has a plurality of sets of characters uniformlyspaced on said disc.
 4. Structure as specified in claim 2 wherein, theradius of said spiral configuration relative to the axis of said disc isequal to Ro + K theta , where Ro is the shortest radius of saidconfiguration, K is a constant, and theta is the angle subtended by theradius of said spiral configuration and Ro.
 5. Structure as specified inclaim 4 wherein said characters are transparent.